Thousands flee Syrian rebel-held town as 'major assault' looms

A man and three boys, covered with dust, sit in a state of shock following a reported air strike attack by government forces on the Hanano district of the northern Syrian city of Aleppo. (AFP)

Thousands of people have fled a rebel-held town in Syria after it was bombed and shelled in an operation that has prompted fears of a major assault by ground troops, the United Nations said.

The fighting came as peace talks in Geneva neared the end of a second round with the government and opposition sides sticking to their positions and as far from agreement as ever.

Violence has spiralled as each side seeks the upper hand. "Nearly 5,000 people have been killed just since these talks began," a senior US official said in Geneva today.

Military action in the town of Yabroud, in western Syria near the border with Lebanon, would fit with the government's aim of securing a corridor linking Damascus with President Bashar al-Assad's heartland on the Mediterranean coast.

"We have received reports from within Syria that there have been numerous aerial attacks and shelling along with a military build-up around the town, suggesting a major assault by land may be imminent," UN human rights spokesman Rupert Colville said.

Some estimates suggested as many as 40,000 to 50,000 people were still in the town with thousands of others fleeing over the last few days, he said.

Electricity was cut off on Wednesday and field hospitals are short of medical supplies as scores of people require urgent treatment, Colville told a news briefing in Geneva.

Failure to allow civilians to leave would amount to "grave violations" of international humanitarian law by Damascus.

About 500 or 600 fleeing families have already arrived in Arsal, Lebanon, and the UN refugee agency expects a big influx across the border, UNHCR spokeswoman Melissa Fleming said.

Al-Manar television, run by Assad's allies in the Lebanese Shi'ite group Hezbollah, said the Syrian army had advanced in the Yabroud area, seizing control of the town's main road and a nearby border crossing it said was used for smuggling.

In Geneva, international mediator Lakhdar Brahimi told delegates he plans to take the talks into a third round but has not set a date for their resumption, opposition negotiator Ahmad Jakal said.

Brahimi said there would be a further session of talks on Saturday and he would fly to New York shortly to meet UN Secretary General Ban Ki-moon, Jakal told reporters.